Various applications of AC devices, for example in electric automobiles or off-highway heavy duty vehicles, demand the use of inverters (power electronic switching devices) that are capable of handling large current requirements for such applications.
Currently, one solution for meeting these demands is to design application-specific inverters for handling large currents. However, current handling capabilities of application-specific inverters may be extended up to a limit. Furthermore, the design of application-specific inverters may become cost-prohibitive depending on how large of a current they have to be able to handle.
Another solution for meeting these demands is to buy larger and larger off the shelf inverters, if they exist. However, such inverters also have performance limits and may become cost prohibitive depending on how large of a current they have to be able to handle.
Yet another solution for meeting these demands is to combine smaller inverters to form a parallel inverter scheme. Accordingly, two smaller inverters may be combined to form one larger inverter. This solution may be referred to as a current sharing scheme. However, existing current sharing schemes are inefficient because slight variations in the two inverters may result in an imbalance situation which leads to overcurrent/overheating in one or more of the smaller inverters, ultimately resulting in the shutdown of the system.
More specifically, in a current sharing scheme, the switches used in the inverters do not match exactly and they do not share current equally when conducting. Accordingly, the switches may have to be sorted and mated to make sure they match, which is costly and inefficient. Furthermore, the switches in the parallel inverters never switch at exactly the same time. For example, when two switches are commanded to be ON at once, one will always come on first. As such, the ‘first’ switch will carry double the current while the second switch carries zero current. Therefore, the first inverter runs extra hot while the second runs extra cool, leading to overcurrent/overheating in one of the inverters associated with the ‘first’ switch. Solutions to address these problems include introducing special filters and/or special cabling (e.g., individual cables of a required length or inductance) to mitigate the undesirable effects. However, these solutions introduce additional signaling and/or additional hardware components into the system, which increase system complexity, design costs and/or inefficiencies.